AM29PDL128G datasheet(28/71 Pages) AMD

28 / 71 page

October 28, 2004

Am29PDL128G

P R E L IM IN A R Y

1. It permanently sets the device to operate using the

Password Protection Mode. It is not possible to re-

verse this function.

2. It also disables

all further commands to the pass-

word region. All program, and read operations are

ignored.

Both of these objectives are important, and if not care-

fully considered, may lead to unrecoverable errors.

The user must be sure that the Password Protection

method is desired when setting the Password Mode

Locking Bit. More importantly, the user must be sure

that the password is correct when the Password Mode

Locking Bit is set. Due to the fact that read operations

are disabled, there is no means to verify what the

password is afterwards. If the password is lost after

setting the Password Mode Locking Bit, there is no

way to clear the PPB Lock bit.

The Password Mode Locking Bit, once set, prevents

reading the 64-bit password on the DQ bus and further

password programming. The Password Mode Locking

Bit is not erasable. Once Password Mode Locking Bit

is programmed, the Persistent Sector Protection Lock-

ing Bit is disabled from programming, guaranteeing

that no changes to the protection scheme are allowed.

64-bit Password

The 64-bit Password is located in its own memory

space and is accessible through the use of the Pass-

word Program and Verify commands (see “Password

Verify Command”). The password function works in

conjunction with the Password Mode Locking Bit,

which when set, prevents the Password Verify com-

mand from reading the contents of the password on

the pins of the device.

Write Protect (WP#)

The Write Protect feature provides a hardware method

of protecting sectors 0, 1, 268, and 269 without using

ID. This function is provided by the WP# pin and over-

rides the previously discussed Sector Protection/Un-

protection method.

If the system asserts V

IL on the WP# pin, the device

disables program and erase functions in sectors 0, 1,

268, and 269 independent of whether it was previously

protected or unprotected using “High Voltage Sector

Protection” on page 27.

If the system asserts VIH on the WP# pin, the device

reverts to whether sectors 0, 1, 268, and 269 were last

set to be protected or unprotected. That is, sector pro-

tection or unprotection for these sectors depends on

whether the sectors were previously protected or un-

protected using “High Voltage Sector Protection” on

page 27.

Persistent Protection Bit Lock

The Persistent Protection Bit (PPB) Lock is a volatile

bit that reflects the state of the Password Mode Lock-

ing Bit after power-up reset. If the Password Mode

Lock Bit is also set after a hardware reset (RESET#

asserted) or a power-up reset. The ONLY means for

clearing the PPB Lock Bit in Password Protection

Mode is to issue the Password Unlock command. Suc-

cessful execution of the Password Unlock command

clears the PPB Lock Bit, allowing for sector PPBs

modifications. Asserting RESET#, taking the device

through a power-on reset, or issuing the PPB Lock Bit

Set command sets the PPB Lock Bit to a “1” when the

Password Mode Lock Bit is not set.

If the Password Mode Locking Bit is not set, including

Persistent Protection Mode, the PPB Lock Bit is

cleared after power-up or hardware reset. The PPB

Lock Bit is set by issuing the PPB Lock Bit Set com-

mand. Once set the only means for clearing the PPB

Lock Bit is by issuing a hardware or power-up reset.

The Password Unlock command is ignored in Persis-

tent Protection Mode.

High Voltage Sector Protection

Sector protection and unprotection may also be imple-

mented using programming equipment. The proce-

dure requires high voltage (V

ID) to be placed on the

RESET# pin. Refer to Table 1 for details on this proce-

dure. Note: For sector unprotect, all unprotected sec-

tors must first be protected prior to the first sector write

cycle.

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